1. Field of the Invention
This invention relates generally to systems for testing electrical and mechanical energy transfer systems that exhibit vibratory and other responses to electrical or mechanical input energy, and more particularly, to an arrangement that isolates a mechanical or electrical system under test and produces signals and data corresponding to a plurality of operating characteristics of the system under test in response to the input energy.
2. Description of the Related Art
Noise testing of gears to date has been attempted by methods that rigidly mount the gear or axle assemblies in one or more planes. Some other previous attempts chose to have one of the rigidly mounted planes resonate at a frequency sympathetic to gear noise. None of these methods, or any other rigidly mounted test system has been successful. This is due to the lack of repeatability of the previous systems, largely as a result of interacting resonances, and external background noise that is transferred through the rigid mounting system. This is especially true in a production test environment.
These deficiencies in the prior art are most evident in the axle industry. At this time, the only widely accepted way of measuring gear noise is to acquire an assembled axle and install it in a test car. A specially trained individual then drives the car over its typical operating range while carefully listening for axle gear noise. The individual rates the quality of axle gear noise on a scale that is typically 0 to 10. Ten is usually a perfect axle, i.e. one that has no gear noise. This method is made difficult by:
1 The lack of available trained noise rating individuals PA1 2 The cost of test cars. PA1 3 The lack of quality roads or test tracks on which to perform a repeatable and accurate test. PA1 4 The time required for each test. PA1 5 The subjectivity that humans bring into the rating system PA1 driving the gear system under test by application of a rotatory input; PA1 producing a first signal responsive to the torque applied to the gear system under test; PA1 producing first digital data responsive to a first correlation between the first signal and time; PA1 measuring peaks in said first digital data to determine whether the peaks exceeds a predetermined threshold magnitude; and PA1 first subjecting those of the peaks that exceed the predetermined threshold magnitude to harmonic analysis. PA1 producing a second signal responsive to a noise produced by the gear system under test in response to the step of driving; PA1 producing a second digital data responsive to a second correlation between the second signal and time; PA1 identifying peaks in the second digital data that are simultaneous with peaks in said first digital data; PA1 measuring the simultaneous peaks in the second digital data to determine whether they exceed a second predetermined threshold magnitude; and PA1 second subjecting those of the simultaneous peaks in the second digital data that exceed the second predetermined threshold magnitude to harmonic analysis. PA1 establishing predetermined harmonic criteria; and PA1 determining whether the results of the analysis in the step of subjecting conforms to the predetermined harmonic criterial of the step of establishing. PA1 driving the gear system under test by application of a rotatory input; PA1 producing a first signal responsive to the torque applied the gear system under test; PA1 producing a second signal responsive to a noise produced by the gear system under test in response to the step of driving; PA1 producing first digital data responsive to a first correlation between the first signal and time; PA1 producing a second digital data responsive to a second correlation between the second signal and time; PA1 identifying simultaneous peaks in the first and second digital data; PA1 measuring the simultaneous peaks in the first and second digital data to determine whether they exceed a predetermined threshold magnitude; and PA1 subjecting those of the simultaneous peaks that exceed the predetermined threshold magnitude to harmonic analysis. PA1 installing the gear assembly on a mounting arrangement that resiliently permits motion of the gear assembly in a plurality of directions, and that has a resilient frequency characteristic that excludes all natural frequencies of the gear assembly; PA1 applying a torque at the input of the gear assembly, whereby the gear assembly is rotatably operated; PA1 applying a load at the output of the gear assembly; PA1 sensing a predetermined operating characteristic of the gear assembly; PA1 producing a first signal responsive to the predetermined operating characteristic of the gear assembly; PA1 producing a second signal responsive to a noise produced by the gear assembly in response to said step of applying a torque; PA1 producing digital data responsive to a correlation between the first and second signals; PA1 converting the digital data into corresponding frequency components; PA1 subjecting the frequency components to analysis to determine a power spectrum density of the frequency components; and PA1 subjecting the power spectrum density to harmonic analysis.
Typically less than a dozen axles can be tested by a major manufacturer in one shift due to all of the above complications. This low number is not statistically valid when it is considered that most manufacturers make thousands of axles each day. Even with all of the above problems, human testers in cars are the only widely accepted method of axle testing in the industry due to the lack of a better more reliable testing method. This lack of a scientific basis for rating axles and gear systems is made worse when the reader considers that modern cars are extremely quiet, and are evolving to become more quite. This market direction increases the pressure on axle and other gear manufacturers to make their products quieter. There is a need for a system that offers gear and axle manufacturers a repeatable, reliable, accurate and practical way of measuring gear noise in production or laboratory environments.
It is, therefore, an object of this invention to provide a system for testing an energy transfer system, such as a vehicle axle, quickly and inexpensively, and achieving repeatable results.